Kernel-based Virtual Machine (KVM)

Description: KVM is “a full virtualization solution for Linux on x86 hardware containing virtualization extensions.” (KVM Main Page) It can be run on the desktop with GUI managers or on a headless server.

Assumptions:

• Some Red Hat based distro is already installed. (CentOS, Scientific, RHEL, etc)
• This page was written using CentOS 6.6 with GNOME desktop

2015-02-13: These are rough notes and in progress as I learn KVM.

• Install: Virtualization Groups

yum groupinstall "Virtualization*"

Group Explanations This will install the following package groups:

• Virtualization Tools ⇒ Tools for offline virtual image management.
• Virtualization Platform ⇒ Provides an interface for accessing and controlling virtualized guests and containers.
• Virtualization Client ⇒ Clients for installing and managing virtualization instances.
• Virtualization ⇒ Provides an environment for hosting virtualized guests.

For detailed info and a list of packages that will be installed:

yum groupinfo "Virtualization*"

• Install: Additional Useful Packages

yum install bridge-utils dejavu-lgc-sans-fonts tigervnc xorg-x11-xauth

Packages Descriptions

• bridge-utils ⇒ network bridging to allow the VMs to use the host machine's physical interfaces as a bridge.
• dejavu-lgc-sans-fonts ⇒ Fonts for virt-manager (GUI VM manager)
• tigervnc ⇒ VNC to connect locally to VM console
• xorg-x11-xauth ⇒ X11 forwarding through ssh. (Remote virt-manager for headless servers)

• Ensure that the KVM kernel module is loaded

lsmod | grep kvm

• Start the libvirtd service

service libvirtd start

• Enable libvirtd on system boot

chkconfig libvirtd on

• Verify libvirtd is running successfully

service libvirtd status
virsh -c qemu://system list

By default, VMs will be on a private network with no access to the outside world unless they use a physical host network interface as a bridge.

• Turn off NetworkManager, which does not play nice with bridging.

chkconfig NetworkManager off
service NetworkManager stop

• Ensure the network service is enabled and running.

chkconfig network on
service network start

• Create a bridge interface called “br0” that will use the physical interface “eth0” the easy way.

virsh iface-bridge eth0 br0

This will create the new file “ifcfg-br0” and modify “ifcfg-eth0” to look as follows:

/etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE="eth0"
HWADDR="00:04:4B:17:3C:FA"
ONBOOT="yes"
BRIDGE="br0"

/etc/sysconfig/network-scripts/ifcfg-br0

DEVICE="br0"
ONBOOT="yes"
TYPE="Bridge"
BOOTPROTO="dhcp"
STP="on"
DELAY="0"

br0 will be the interface with an IP address. To make it static, simply edit ifcfg-br0 and change it:

DEVICE="br0"
ONBOOT="yes"
TYPE="Bridge"
BOOTPROTO="none"
STP="on"
DELAY="0"
IPADDR="192.168.0.100"
NETMASK="255.255.255.0"
GATEWAY="192.168.0.1"

• Enable ip forwarding

Edit /etc/sysctl.conf

inet.ipv4.ip_forward = 1

• Apply settings

sysctl -p /etc/sysctl.conf

• Restart the network service

service network restart

If SELinux is in Enforcing mode, there is additional configuration if you change the default directory for VM images.

Default VM Image directory: /var/lib/libvirt/images/

• Create the directory

mkdir /vm-images

• Install the following package to enable use of the “semanage” utility.

yum install policycoreutils-python

• Set security context for the vm-images directory and everything that is created under it.

semanage fcontext -a -t virt_image_t "/vm-images(/.*)?"

• Restore the security context (I don't know why you have to do this yet…but you do)

restorecon -R /vm-images

• Verify

ls -Z /vm-images

VMs can be installed via a command line tool (virt-install) or a GUI (virt-manager).

virt-install has many options, see them with “virt-install –help”.

Common options:

General Options
--name=NAME  (Name of the guest)
--ram=MEMORY  (Memory in megabytes)
--vcpus=VCPUS  (Number of vcpus)
 
Installation Method
--cdrom=CDROM  (CD-ROM installation media, can be ISO or physical cd-rom drive)
--location=LOCATION  (Installation source via http, ftp, or nfs.)
--pxe  (Boot from network using PXE)
--extra-args "ks=http://myserver/mykickstartfile.ks"  (Path to kickstart file for automated installs)
 
Storage Configuration
--disk=DISKOPTS  (Storage with different options)
  --disk path=/my/existing/disk 
  --disk path=/my/new/disk,size=10 (in GB)
 
Network
--network bridge=br0  (Guest network interface)
 
Graphics
--graphics=GRAPHICS  (Guest display settings)
  --graphics vnc  (Default if DISPLAY environment variable is set)
  --graphics none  (Default if DISPLAY environment variable is not set)

Install a VM called “centos1”, create a 20GB hard drive, 1 CPU, 1GB ram, point it to the iso, have it use the network interface “br0”

virt-install \
--name=centos1 \
--disk path=/vm-images/centos1.img,size=20 \
--vcpus=1 --ram=1024 \
--cdrom=/vm-images/CentOS-6.6-x86_64-netinstall.iso \
--network bridge=br0

After the VM is created, if you are using the “–graphics vnc” option (either by default or explicitly), a console is opened up for interactive install.

If you close it, this is how you can connect back to the guest:

• Method 1: Connect directly to the guest console

Example connect to the guest named “centos1” (Yes, that is 3 slashes)

virt-viewer --connect qemu:///system centos1

• Method 2: Open virt-manager

Example open virt-manager and then the VM “centos1”

virt-manager

• Select the VM
• Click “Open”

Proceed with installation as normal.

Installing locally via a GUI.

• Open a terminal and type:

virt-manager

• The virt-manager GUI will open.
• Select the name of the host (probably “localhost (QEMU)”)
• Click the “Create a New Virtual Machine” button (the monitor with a play button on it)
  • Step 1 ⇒
    • Name: Name the virtual machine
    • Choose how to install: Select the install method
  • Step 2 ⇒
    • Browse for the media
    • OS Type/Version: Optionally, select the OS type and version
  • Step 3 ⇒
    • Memory/CPU: Select memory and CPU.
  • Step 4 ⇒
    • Storage: Create or use existing storage
  • Step 5 ⇒
    • Ready to install: Confirm settings, set advanced options such as Host network device.